This invention relates to means for automatically releasing a packed parachute canopy to deploy the canopy in chosen circumstances, and is particularly, but not exclusively, concerned with means for automatically releasing a secondary parachute in the event that a primary parachute has failed to deploy correctly or fails after deployment during a descent.
Automatic parachute release devices have been proposed to release a main parachute canopy at a predermined height above the ground during a so called free fall parachute drop, either as the primary means of releasing the canopy or as a safety back-up to cover the event of error or incapacity of a parachutist. The basic design of such release mechanisms includes a barometric capsule arranged to move a locking pin which retains an operating arm of the parachute release mechanism thus allowing movement of the operating arm to release the canopy. The release height is adjusted by adjusting the position of the capsule and pin relative to the release arm; and as the capsule is fully evacuated adjustment is made allowing for the ambient barometric pressure immediately before use.
In order to cover the event that the canopy fails to deploy at the desired height, typically 1000 meters (3000 feet) above ground, or collapses after deployment; a secondary or reserve parachute is usually carried, and means is provided to automatically deploy the secondary canopy once below the chosen height in the event of failure of the primary canopy. The release means for the secondary canopy detects failure of the main canopy by detecting an abnormal rate of descent and must of course be inhibited from operating during any free fall phase of a drop. A rate of fall in excess of typically 25 meters per second (70 feet per second) is considered indicative of a canopy failure or malfunction; and below 1000 metres this corresponds to a rate of pressure change of 2.3 to 2.5 millibars per second.
Devices so far proposed to respond to such rates of change of pressure have involved the use of very sensitive sensing diaphrams, and these devices have been prone to respond to transient pressure pulses releasing the secondary canopy erroneously. With known devices it is thought that even the small transient pressure pulses that might arise within the parachutist's clothing during normal movement, could erroneously cause release of the secondary canopy.